Apache ZooKeeper

官方文檔

zk入門指南

閱讀本文檔能使您快速瞭解並使用ZooKeeper。主要內容包含：

瞭解ZooKeeper的相關的概念

下載安裝ZooKeeper服務

Zookeeper的配置、啓動與客戶端連接

瞭解ZooKeeper的一些簡單命令

什麼是ZooKeeper？

ZooKeeper翻譯成中文的意思是動物管理員，它是一個分佈式服務框架，用於維護配置信息，提供統一命名，分佈式狀態同步，集羣管理等服務。

基本概念

爲了更快的掌握zookeeper，我們首先需要了解zookeeper中的一些基本概念，例如集羣角色（leader、follower、observer）,會話（session）,數據節點（ZNode）,狀態信息,事務操作,事件監聽器（watcher）,ACL

集羣角色

leader：負責進行投票的發起和決議，更新系統狀態
follower：接收客戶端請求，參與投票
observer：接收客戶端請求，將寫請求轉發給leader，不參加投票過程，只同步leader的狀態，observer的目的是爲了擴展系統，提高讀取速度

Session

session是指客戶端和zookeeper服務器之間的一個TCP長連接。從第一次建立連接開始，客戶端session會話生命週期就開始了。client可以通過心跳監測和服務器保持有效的會話，同時也可以通過該連接接收服務器的watch事件通知。

ZNode

zookeeper中的ZNode稱爲數據節點。是指數據模型中的數據單元。ZNode是一個樹，由斜槓（/）分隔路徑，例如：/hbash/master/ 其中，hbash和 master分別都是一個ZNode，在自己的ZNode中保存自己的數據。可以簡單的將ZNode理解爲Unix的文件系統。

3.1 節點類型

持久節點：必須主動刪除纔會失效

臨時節點：會話失效時就會失效。

3.2 版本

zookeeper會爲每個ZNode維護一個Stat的數據結構，在該結構中記錄了ZNode的三個版本

version - 當前版本
cversion - 當前ZNode的子節點的版本
aversion - 當前ZNode的ACL版本（ACL : 訪問控制列表）

事務

在zookeeper中，把改變zookeeper服務器狀態的操作稱爲事務操作。一般包括ZNode節點的創建與刪除、數據內容的更新、客戶端session的建立與失效等操作。每一個事務請求，zk都會爲其分配一個全局的事務ID，用ZXID表示，通常是一個64位的數字（它高32位是epoch用來標識 leader關係是否改變，每次一個leader被選出來，它都會有一個新的epoch，標識當前屬於那個leader的統治時期。低32位用於遞增計數。）。每一個ZXID對應的一次更新操作，從這些ZXID中可以間接識別出zk處理這些事務操作的全局順序一致性。

Watcher

watcher即事件監聽器，是zk中的一個重要的分佈式協調的特性。zk允許用戶在指定節點註冊一些watcher，並在特定事件觸發時，zk會將通知到指定客戶端上。

ACL

ACL全稱爲access control lists ，是zk的一種權限控制策略。zk定義瞭如下5中權限：

create ：創建子節點的權限
read：獲取節點數據和子節點列表
write：更新節點數據
delete：刪除子節點
admain：設置節點ACL權限

下載

因爲zookeeper依賴JDK，所以需要先下載安裝JDK。沒有安裝JDK的同學移步教程---->>> 一分鐘搞定JDK的安裝與配置

JDK8：JDK8的下載地址

Apache最新穩定版：zookeeper官網鏡像地址

TIPS：選擇版本下載一定要注意選擇帶bin的安裝包，否則下載錯文件可能導致zkServer.sh start無法啓動。

或點擊直接下載：apache-zookeeper-3.6.2-bin.tar.gz

安裝

下載好apache-zookeeper-3.6.2.tar.gz後，在根目錄創建servers目錄，我們稍後把zk安裝到這裏方便管理。

解壓

執行命令，tar -xvzf 解壓，加-C ~/servers的作用是指定目錄

tar -xvzf apache-zookeeper-3.6.2.tar.gz -C ~/servers/ ```

2. 爲zk建立軟連接
* 進入servers目錄
```bash
[lb@centos-linux servers]$ ln -s apache-zookeeper-3.6.2 zookeeper
[lb@centos-linux servers]$ ls
apache-zookeeper-3.6.2  zookeeper

到此爲止，我們的zk就安裝成功了。看一下目錄結構

[lb@centos-linux zookeeper]$ pwd
/home/lb/servers/zookeeper
[lb@centos-linux zookeeper]$ ls
bin                         excludeFindBugsFilter.xml  pom.xml              zookeeper-compatibility-tests  zookeeper-recipes
checkstyle-simple.xml       Jenkinsfile                README.md            zookeeper-contrib              zookeeper-server
checkstyle-strict.xml       Jenkinsfile-PreCommit      README_packaging.md  zookeeper-docs
checkstyleSuppressions.xml  LICENSE.txt                zk-merge-pr.py       zookeeper-it
conf                        NOTICE.txt                 zookeeper-assembly   zookeeper-jute
dev                         owaspSuppressions.xml      zookeeper-client     zookeeper-metrics-providers
[lb@centos-linux zookeeper]$

配置

進入/zookeeper/conf/目錄，拷貝zoo_sample.cfg 文件，拷貝爲一個新的配置：zoo.cfg

cp zoo_sample.cfg zoo.cfg

編輯zoo.cfg，修改dataDir配置，wq保存並退出

dataDir=/home/lb/servers/zookeeper/data

返回zookeeper目錄，新建data文件夾

-p, --parents 需要時創建目標目錄的上層目錄，但即使這些目錄已存在也不當作錯誤處理 -v, --verbose 每次創建新目錄都顯示信息

mkdir -p -v data

配zk的環境變量

編輯bash_profile ，新增如下配置：

export ZOOKEEPER_HOME=/home/lb/servers/zookeeper
PATH=$ZOOKEEPER_HOME/bin:$PATH

最終的配置如下：

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs
export JAVA_HOME=/home/lb/package/java
export ZOOKEEPER_HOME=/home/lb/servers/zookeeper

PATH=$PATH:$HOME/.local/bin:$HOME/bin
PATH=$JAVA_HOME/bin:$PATH
PATH=$ZOOKEEPER_HOME/bin:$PATH

export PATH

使配置生效 source ~/.bash_profile

開始使用

啓動zkServer

執行命令 zkServer.sh start

# 查看zkServer有哪些命令
[lb@centos-linux conf]$ zkServer.sh
ZooKeeper JMX enabled by default
Using config: /home/lb/servers/zookeeper/bin/../conf/zoo.cfg
Usage: /home/lb/servers/zookeeper/bin/zkServer.sh [--config <conf-dir>] {start|start-foreground|stop|version|restart|status|print-cmd}
# 啓動zk服務
[lb@centos-linux conf]$ zkServer.sh start
ZooKeeper JMX enabled by default
Using config: /home/lb/servers/zookeeper/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED
[lb@centos-linux conf]$
# 查看zk服務狀態
[lb@centos-linux conf]$ zkServer.sh status
ZooKeeper JMX enabled by default
Using config: /home/lb/servers/zookeeper/bin/../conf/zoo.cfg
Client port found: 2181. Client address: localhost. Client SSL: false.
Mode: standalone # 單機版
[lb@centos-linux conf]$

客戶端連接zkServer

直接執行zkCli.sh

zkCli.sh
Connecting to localhost:2181
2020-12-18 09:59:43,848 [myid:] - INFO  [main:Environment@98] - Client environment:zookeeper.version=3.6.2--803c7f1a12f85978cb049af5e4ef23bd8b688715, built on 09/04/2020 12:44 GMT
2020-12-18 09:59:43,850 [myid:] - INFO  [main:Environment@98] - Client environment:host.name=centos-linux.shared
2020-12-18 09:59:43,850 [myid:] - INFO  [main:Environment@98] - Client environment:java.version=1.8.0_271
2020-12-18 09:59:43,851 [myid:] - INFO  [main:Environment@98] - Client environment:java.vendor=Oracle Corporation
2020-12-18 09:59:43,851 [myid:] - INFO  [main:Environment@98] - Client environment:java.home=/home/lb/package/jdk1.8.0_271/jre
2020-12-18 09:59:43,851 [myid:] - INFO  [main:Environment@98] - Client environment:java.class.path=/home/lb/servers/zookeeper/bin/../zookeeper-server/target/classes:/home/lb/servers/zookeeper/bin/../build/classes:/home/lb/servers/zookeeper/bin/../zookeeper-server/target/lib/*.jar:/home/lb/servers/zookeeper/bin/../build/lib/*.jar:/home/lb/servers/zookeeper/bin/../lib/zookeeper-prometheus-metrics-3.6.2.jar:/home/lb/servers/zookeeper/bin/../lib/zookeeper-jute-3.6.2.jar:/home/lb/servers/zookeeper/bin/../lib/zookeeper-3.6.2.jar:/home/lb/servers/zookeeper/bin/../lib/snappy-java-1.1.7.jar:/home/lb/servers/zookeeper/bin/../lib/slf4j-log4j12-1.7.25.jar:/home/lb/servers/zookeeper/bin/../lib/slf4j-api-1.7.25.jar:/home/lb/servers/zookeeper/bin/../lib/simpleclient_servlet-0.6.0.jar:/home/lb/servers/zookeeper/bin/../lib/simpleclient_hotspot-0.6.0.jar:/home/lb/servers/zookeeper/bin/../lib/simpleclient_common-0.6.0.jar:/home/lb/servers/zookeeper/bin/../lib/simpleclient-0.6.0.jar:/home/lb/servers/zookeeper/bin/../lib/netty-transport-native-unix-common-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/netty-transport-native-epoll-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/netty-transport-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/netty-resolver-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/netty-handler-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/netty-common-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/netty-codec-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/netty-buffer-4.1.50.Final.jar:/home/lb/servers/zookeeper/bin/../lib/metrics-core-3.2.5.jar:/home/lb/servers/zookeeper/bin/../lib/log4j-1.2.17.jar:/home/lb/servers/zookeeper/bin/../lib/json-simple-1.1.1.jar:/home/lb/servers/zookeeper/bin/../lib/jline-2.14.6.jar:/home/lb/servers/zookeeper/bin/../lib/jetty-util-9.4.24.v20191120.jar:/home/lb/servers/zookeeper/bin/../lib/jetty-servlet-9.4.24.v20191120.jar:/home/lb/servers/zookeeper/bin/../lib/jetty-server-9.4.24.v20191120.jar:/home/lb/servers/zookeeper/bin/../lib/jetty-security-9.4.24.v20191120.jar:/home/lb/servers/zookeeper/bin/../lib/jetty-io-9.4.24.v20191120.jar:/home/lb/servers/zookeeper/bin/../lib/jetty-http-9.4.24.v20191120.jar:/home/lb/servers/zookeeper/bin/../lib/javax.servlet-api-3.1.0.jar:/home/lb/servers/zookeeper/bin/../lib/jackson-databind-2.10.3.jar:/home/lb/servers/zookeeper/bin/../lib/jackson-core-2.10.3.jar:/home/lb/servers/zookeeper/bin/../lib/jackson-annotations-2.10.3.jar:/home/lb/servers/zookeeper/bin/../lib/commons-lang-2.6.jar:/home/lb/servers/zookeeper/bin/../lib/commons-cli-1.2.jar:/home/lb/servers/zookeeper/bin/../lib/audience-annotations-0.5.0.jar:/home/lb/servers/zookeeper/bin/../zookeeper-*.jar:/home/lb/servers/zookeeper/bin/../zookeeper-server/src/main/resources/lib/*.jar:/home/lb/servers/zookeeper/bin/../conf:
2020-12-18 09:59:43,851 [myid:] - INFO  [main:Environment@98] - Client environment:java.library.path=/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:java.io.tmpdir=/tmp
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:java.compiler=<NA>
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:os.name=Linux
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:os.arch=amd64
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:os.version=3.10.0-327.el7.x86_64
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:user.name=lb
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:user.home=/home/lb
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:user.dir=/home/lb/servers/apache-zookeeper-3.6.2-bin/conf
2020-12-18 09:59:43,852 [myid:] - INFO  [main:Environment@98] - Client environment:os.memory.free=23MB
2020-12-18 09:59:43,853 [myid:] - INFO  [main:Environment@98] - Client environment:os.memory.max=228MB
2020-12-18 09:59:43,853 [myid:] - INFO  [main:Environment@98] - Client environment:os.memory.total=29MB
2020-12-18 09:59:43,857 [myid:] - INFO  [main:ZooKeeper@1006] - Initiating client connection, connectString=localhost:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@1175e2db
2020-12-18 09:59:43,863 [myid:] - INFO  [main:X509Util@77] - Setting -D jdk.tls.rejectClientInitiatedRenegotiation=true to disable client-initiated TLS renegotiation
2020-12-18 09:59:43,872 [myid:] - INFO  [main:ClientCnxnSocket@239] - jute.maxbuffer value is 1048575 Bytes
2020-12-18 09:59:43,881 [myid:] - INFO  [main:ClientCnxn@1716] - zookeeper.request.timeout value is 0. feature enabled=false
Welcome to ZooKeeper!
2020-12-18 09:59:43,892 [myid:localhost:2181] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1167] - Opening socket connection to server localhost/127.0.0.1:2181.
2020-12-18 09:59:43,892 [myid:localhost:2181] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1169] - SASL config status: Will not attempt to authenticate using SASL (unknown error)
2020-12-18 09:59:43,896 [myid:localhost:2181] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@999] - Socket connection established, initiating session, client: /127.0.0.1:39308, server: localhost/127.0.0.1:2181
JLine support is enabled
2020-12-18 09:59:43,923 [myid:localhost:2181] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1433] - Session establishment complete on server localhost/127.0.0.1:2181, session id = 0x10000fc83a10000, negotiated timeout = 30000

WATCHER::

WatchedEvent state:SyncConnected type:None path:null
[zk: localhost:2181(CONNECTED) 0]

[zk: localhost:2181(CONNECTED) 0]說明連接成功了！

一些簡單命令

查看節點目錄

命令：ls <節點名稱>

[zk: localhost:2181(CONNECTED) 0] ls /
[zookeeper]

查看zookeeper節點下有哪些節點

[zk: localhost:2181(CONNECTED) 1] ls /zookeeper
[config, quota]

查看quota節點的子節點,結果爲[ ] 說明沒有子節點

[zk: localhost:2181(CONNECTED) 8]  ls /zookeeper/quota
[]

查看節點屬性

命令：get -s <節點名稱>

查看zookeeper節點有哪些屬性

[zk: localhost:2181(CONNECTED) 17] get -s /zookeeper
                      # 節點內容，這裏爲空
cZxid = 0x0
ctime = Thu Jan 01 08:00:00 CST 1970
mZxid = 0x0
mtime = Thu Jan 01 08:00:00 CST 1970
pZxid = 0x0
cversion = -2
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 0
numChildren = 2

查看quota數據節點有哪些屬性

[zk: localhost:2181(CONNECTED) 21] get -s /zookeeper/quota

cZxid = 0x0
ctime = Thu Jan 01 08:00:00 CST 1970
mZxid = 0x0
mtime = Thu Jan 01 08:00:00 CST 1970
pZxid = 0x0
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 0
numChildren = 0

添加數據節點

命令：create <數據節點路徑及名稱> <數據節點內容>

在根目錄添加一個home節點，節點內容爲123

[zk: localhost:2181(CONNECTED) 22] create /home 123
Created /home
#查看home節點屬性
[zk: localhost:2181(CONNECTED) 23] get -s /home 
123 #節點內容
cZxid = 0x2
ctime = Fri Dec 18 10:23:11 CST 2020
mZxid = 0x2
mtime = Fri Dec 18 10:23:11 CST 2020
pZxid = 0x2
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 3
numChildren = 0

修改數據節點

命令：set <數據節點名稱> <數據內容>

修改數據節點home的值爲123456

[zk: localhost:2181(CONNECTED) 24] set /home 123456
[zk: localhost:2181(CONNECTED) 25] get -s /home
123456
cZxid = 0x2
ctime = Fri Dec 18 10:23:11 CST 2020
mZxid = 0x3 #mZxid+1
mtime = Fri Dec 18 10:25:46 CST 2020 # 時間更新
pZxid = 0x2
cversion = 0
dataVersion = 1 #版本+1
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 6 #數據長度更新
numChildren = 0

刪除數據節點

語法：delete <數據節點路徑>

tips：只有沒有子節點的節點才允許刪除，例如如下案例：

home節點下創建了一個n1節點

[zk: localhost:2181(CONNECTED) 36] create /home/n1 ''
Created /home/n1
[zk: localhost:2181(CONNECTED) 38] ls /home
[n1]

刪除home節點，會提示Node not empty: /home

[zk: localhost:2181(CONNECTED) 40] delete /home
Node not empty: /home

刪除n1節點，沒有問題，刪除成功

[zk: localhost:2181(CONNECTED) 41] delete /home/n1
[zk: localhost:2181(CONNECTED) 42] ls /home
[]

恭喜你！關於zookeeper的簡單入門就到到此爲止啦！

如果想了解更多關於ZooKeeper的高階知識，請閱讀：

ZooKeeper入門指南

Apache ZooKeeper

zk入門指南

什麼是ZooKeeper？

基本概念

集羣角色

Session

ZNode

事務

Watcher

ACL

下載

安裝

配置

開始使用

啓動zkServer

客戶端連接zkServer

一些簡單命令

查看節點目錄

查看節點屬性

添加數據節點

修改數據節點

刪除數據節點

恭喜你！關於zookeeper的簡單入門就到到此爲止啦！

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